Ocean acidification feedback causes increased warming

27 03 2014
Mark Cochrane

Mark Cochrane

Another guest post from Mark Cochrane…… who continues bringing bad news after a few months of more research.

I’ve posted before on the “other CO2 problem”, namely ocean acidification but up until recently, ocean acidification and greenhouse gas-related warming of the planet have been seen as problematic but separate processes happening due to our fossil fuel-related binge of carbon emissions.

For those who don’t know, ocean acidification arises when CO2 is forced into ocean waters, sort of like in your soda or beer. We increase atmospheric concentrations of CO2, this forces some of the gas into solution in the ocean surface layer. The carbon dioxide then reacts with water molecules to form carbonic acid.

Acidity is measured in units of pH. The ocean’s pH has fallen by a little more than 0.1 pH units since the beginning of the Industrial Revolution which doesn’t sound terribly impressive but the scale is logarithmic, meaning that changes are exponential in terms of their magnitude. You might have some idea of what that means if you think in terms of the Richter scale of earthquake intensity which is also logarithmic, with each additional 1.0 meaning 10 times the shaking magnitude and 31.6 times the energy release. Back to the ocean pH, that measly 0.11 change equates to a 30% increase in the global ocean’s acidity levels.

That is a very significant change in such a short time for organisms like oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton. If we continue on the path of “Business as Usual” carbon emissions then we will make the ocean’s surface waters 150% more acidic by the end of the century. Nothing like this has been seen for more than 20 million years. This is what those acidity levels will do to current organisms living in the oceans.

Where this impacts the global climate is by messing up the oceanic sulfur cycle. Phytoplankton release something called DMS (dimethyl sulfide). DMS goes into the atmosphere above the oceans and forms cloud condensation nuclei (CCNs). In layman’s terms, the DMS seeds low level clouds over the oceans. These clouds act to reflect a portion of the sunlight from the Earth and thereby cool the planet.

So what we have is the following chain of events. Continued CO2 emissions raise atmospheric CO2 levels which in turn raise aqueous CO2 levels in the oceans. This then lowers the ocean’s pH (increased acidity) which stresses or kills phytoplankton. Less phytoplankton results in less DMS. Less DMS yields less clouds over the oceans. Less clouds means more sunlight warms the oceans and hence the exacerbates global climate change. Multiple experiments in sea water exclosures (mesocosms) have verified this impact. Which leads us to this recent scientific finding:

Global warming amplified by reduced sulphur fluxes as a result of ocean acidification

Global DMS emissions decrease by about 18(±3)% in 2100 compared with pre-industrial times as a result of the combined effects of ocean acidification and climate change. The reduced DMS emissions induce a significant additional radiative forcing, of which 83% is attributed to the impact of ocean acidification, tantamount to an equilibrium temperature response between 0.23 and 0.48K. Our results indicate that ocean acidification has the potential to exacerbate anthropogenic warming through a mechanism that is not considered at present in projections of future climate change.  (Six et al. 2013)

For those who don’t know 0.23-0.48 K (Kelvin) is the same as 0.23-0.48 C (Celsius).

This is yet another positive feedback that will likely make the rate of climate changes more rapid than current values given in global climate models. Those who have an issue with models should understand that if the models are ‘wrong’, they are at least as likely to be understating the rate of climate change as overstating it. The impacts of the rapid acidification though will be the real problem for life in the oceans. Eventually life in the oceans would adapt to the higher acidity but it is happening so fast that evolution cannot keep pace. There will be serious consequences for all life because of this on any time scale significant to human societies.



9 responses

27 03 2014
Dave Kimble

It’s a good job that Peak Fossils is nearly on us, so “Business As Usual” won’t happen and none of those scary things will happen.

The role of phytoplankton (not to be confused with those things in the pictures) in the ocean is an area of much scientific disagreement, so “this scientific finding” shouldn’t be presented as if it was scientifically proven. It sounds like a small-scale experiment, using environmental parameters projected for 2100 under BAU fossil burning, so is completely meaningless.

Despite 400 ppm(CO2), in some parts of the ocean phytoplankton numbers are increasing. Some geo-engineering advocates suggest increasing Iron in the oceans to help them increase further, as their photosynthesis takes up CO2, and is limited most by iron availability.

1 04 2014
Mulga Mumblebrain

Where, precisely, are phytoplankton numbers increasing, and, if known, why?

1 04 2014

Phytoplankton exist in all oceans and have done for billions of years. They need sunlight to grow and reproduce, so their numbers vary with seasons – most growth in the spring. They also need dissolved CO2, a seasonal factor, so higher levels of CO2 are not a serious problem. They also respond to temperature change, which is another seasonal factor. They also need other nutrients, so nutrient rich ocean upwellings affect populations.

Complicating matters are the zooplankton, which eat the phytoplankton, and so have population fluctuations of their own, usually peaking after phytoplankton’s peak. And so on up the trophic chain.

So the question “Where precisely…” is impossible to answer, but probably in areas of ocean upwelling, with good sunlight (no clouds), warmer than usual, more CO2 than usual – blooms of phytoplankton can be photographed from satellites.

7 04 2014
Mulga Mumblebrain

Thanks falloy-I may have confused the phytoplankton with the zooplankton. But, tell me, do warming, acidified oceans benefit the phytos without negative consequences? Will disruptions to oceanic circulation not be negative? I would have thought so.

7 04 2014

The consequences would be different from place to place, but generally characterised by a change to the species composition – more of those that like the new conditions, less of those that don’t. At the very extremes of temperature, a very seasonal thing, some species may not cope and go locally extinct, while surviving elsewhere. Numbers breed up quickly, and natural variation should drive selection of the fittest.

The same thing will apply to the zooplankton, and the things that feed on them. Higher up the food chain, fish and whales are slower breeding, so can’t evolve so quickly. “Negative consequences” imply stability is good, and change is bad, but that rather depends on how you assess consequences.

It’s only 18,000 years since the last ice age, so everything you see now in the Arctic wasn’t like that 18,000 years ago. Has the change brought negative consequences?

8 04 2014
Mulga Mumblebrain

Yes, palloy, I appreciate that these populations are very dynamic and can adapt rapidly, but is not the current problem one of the rate of change. Is it not the rapid rise of temperatures to unprecedented levels and of acidification, and the ‘unknown unknowns’ that will flow from these and other rapid destabilisations, that are the crucial factors?

8 04 2014

Temperatures in the Arctic summer vary on a daily cycle, like everywhere else, and so for most of the time temperatures are within the limits of what phytoplankton are used to. It is only for a few hours a day that the peak temperature might make them uncomfortable, and those near the surface will suffer most, while those at deeper levels will remain OK, but get less sunlight, so won’t grow so much.

Meanwhile reproduction, with variation, still proceeds and selection for high temperature tolerance speeds up. Because the rate of evolution of Phytoplankton is so fast, it easily outpaces the rate of temperature change and the rate of acidification due to climate change. As you go further up the food chain, the species cannot react/evolve so fast, so you would expect to see effects show up there first. But fish and whales etc. don’t like swimming below sea ice, so loss of ice is better for them, all other things being equal.

The net result is a more dynamic species composition. The unknown unknowns are unknown, but there is no reason to suppose they will be bad unknowns or big, bad unknowns, unless you enjoy scary stories just for the sake of it.

30 03 2014
Ocean acidification feedback causes increased warming | Agriculture and Climate Change

[…] Ocean acidification feedback causes increased warming. […]

23 06 2014

1 Sea water is not acidic but alkaline. I tell it because you don’t. So called sea water acidification is change is toward neutral.
2. There is not enought fossil carbon in Earth to change sea water acidic even if it all will be burn.
3. Upwellings are main reason for “acificifation” problems.
4. Focusing only positive feedbacks give biassed picture.

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